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The spread of cheap, powerful cameras capable of reading license plates has allowed police to
build databases on the movements of millions of Americans over months or even years, according to
an
American Civil Liberties Union report released today.

The license-plate readers, which police typically mount along major roadways or on the backs
of cruisers, can identify vehicles almost instantly and compare them against “hot lists” of cars
that have been stolen or involved in crimes.

But the systems collect records on every license plate they encounter - whether or not they
are on hot lists - meaning time and location data are gathered in databases that can be searched by
police. Some departments purge information after a few weeks, some after a few months and some
never, said the report, which warns that such data could be abused by authorities, and chill
freedom of speech and association.

“Using them to develop vast troves of information on where Americans travel is not an
appropriate use,” said Catherine Crump, a staff attorney at the ACLU and one of the authors of the
report, “You are Being Tracked: How License Plate Readers Are Being Used to Record Americans’
Movements.”

The use of license-plate readers is common in the Washington area, where concerns about
terrorism have fueled major investments in the equipment, with much of the money coming from
federal grants. Agreements among departments and jurisdictions allow sharing of the location
information, with data typically retained for at least a year.

Such details, say police and law enforcement experts, can help investigators reconstruct
suspects’ movements before and after armed robberies, auto thefts and other crimes. Departments
typically require that information be used only for law enforcement purposes and require audits
designed to detect abuse.

“We’d like to be able to keep the data as long as possible, because it does provide a rich
and enduring data set for investigations down the line,” said David Roberts, senior program manager
for the Technology Center of the International Association of Chiefs of Police.

But the ACLU argues that data collection by most police departments is unnecessarily broad.
In an analysis of data collected in Maryland, the report found that license-plate readers recorded
the locations of vehicle plates 85 million times in 2012.

Based on a partial-year analysis of that data, the ACLU found that about one in 500 plates
registered hits. In the overwhelming majority of cases, it said, the alleged offenses were minor,
involving lapsed registrations or failures to comply with the state’s emission-control program.

For each million plates read in Maryland, 47 were associated with serious crimes, such as a
stolen vehicle or a wanted person, the report said. Statistics collected by the ACLU in several
other jurisdictions around the country also found hit rates far below 1 percent of license plates
read.

Maryland officials have defended their program, which collects data from departments across
the state in a fusion center, which shares intelligence among federal, state and local agencies. In
a recent three-month period, state officials said, license-plate readers contributed to 860 serious
traffic citations and the apprehension of 180 people for crimes including stolen autos or license
plates.

The center deletes the data one year after they are collected, in what officials said was a
compromise between investigative needs and privacy rights.

“We don’t want to retain more information . . . than is necessary,” said Harvey Eisenberg, an
assistant U.S. attorney who oversees Maryland’s Anti-Terrorism Advisory Council. “You strike the
balance, because people are legitimately concerned.”

The license-plate readers are also widely used in Washington and the Virginia suburbs, where
they are mounted on many of the major roadways entering and exiting the city. A District of
Columbia police spokeswoman did not immediately comment on the ACLU report.

Private companies also are using license-plate-reading technology to build databases,
typically to help in repossessing cars.